The long-range goal of this project is to understand, in physical chemical terms, how bacterial viruses are assembled. These are perhaps the most complex supramolecular assemblies currently susceptible to detailed molecular understanding. As such they serve as realistic models for the regulation of morphogenesis of cell organelles in higher organisms. We concentrate on T4 phage, and in the next project period have these specific aims: 1. Determine the ways in which baseplate proteins gp48 and gp54 interact with the baseplate, with each other and with the tail tube protein gp19 to regulate the length of the tail tube of T4 phage. 2. Determine the propagation and termination mechanisms for tube polymerization, by investigating the kinetics of polymerization, searching for oligomeric intermediates of gp19 and determining whether it undergoes a conformational change upon polymerization. 3. Determine the extent of similarity between tail fibers and non-muscle myosin, with respect to chemical and physical structure, reactivity, and enzymatic activity; and search for actin-like proteins (of which gp63 may be one) in T4. 4. Determine the mechanism of attachment of tail fibers to basepolates, elucidating the structures, energetics, an dynamics of the complexes with gp63 and whiskers. 5. Determine the forces stabilizing DNA inside phage capsids, especially the role of polycations, using polyelectrolyte and intermolecular force theories. To accomplish these aims we shall prepare phage components from appropriate mutants, purify them by standard biochemical techniques, and assay both chemically and by in vitro complementation. The major physical tools will be laser light scattering and hydrodynamics; but we will also use electron microscopy, circular dichroism, chemical crosslinking, and various tests of protein-protein interaction.